Mine does something similar. When started from hot, idle will drop to 450/500, then speed up to 1000. Continuing this pulsing it will sometimes stall. Strangely, when you drive it for a few minutes, it will idle properly.

Mine does something similar. When started from hot, idle will drop to 450/500, then speed up to 1000. Continuing this pulsing it will sometimes stall. Strangely, when you drive it for a few minutes, it will idle properly.

The bulb on the throttle body that prevents the blade from slamming shut in the TB bore and sticking closed. It's on the left side, and has a white plastic plunger that contacts the throttle linkage. Adjusted with a jam nut/threading. Back it off a bit and see if it helps the situation.

I had an issue on one of my engines where the dashpot would pop the throttle open, it would rev up and build vacuum, suck the plate closed, idle down, less vac, pop open, cycle repeated.